Bacteria are the primary cause of plaque-associated gingivitis and chronic adult periodontitis. It is unclear, however, whether the microorganisms responsible for gingivitis also contribute to the development of adult periodontitis or whether a unique assemblage of microorganisms is responsible for periodontitis. Studies indicate that plaque-associated gingivitis progresses to chronic adult periodontitis in only a subset of individuals. Previous work on this topic has been hampered by the limitations of cultivation-based methods, taxonomic inconsistencies, insufficient microbial characterization and inter-patient heterogeneity. The proposed work relies upon sensitive molecular methods to identify predictive associations between specific bacterial and archaeal species and the onset of adult periodontitis. The short-term objectives are to determine the subgingival microbial markers of gingival health, plaque-associated gingivitis and chronic adult periodontitis. The long-term objectives are to understand oral microbial ecology, to determine its relationship with local and systemic disease, and by so doing, to identify healthy individuals with increased risk of disease who would benefit from early intervention. The Specific Aims of this proposal are: Aim 1. Identify the bacterial and archaeal species within subgingival plaque from healthy sites in periodontitis patients. Phylogenetic analysis of 16S ribosomal DNA sequences and high density DNA microarrays will be used to identify the microbial species composition of subgingival plaque. Aim 2. Identify the bacteria and archaea from plaque-associated gingivitis and chronic adult periodontitis sites using the approach in Aim 1. Aim 3. Quantify differences in bacterial and archaeal contribution to the total microbial population within subgingival plaque associated with healthy gingiva, plaque-associated gingivitis and chronic adult periodontitis. Slot-blot and in situ hybridization methods will be applied with group- and species-specific 16S rDNA probes. Targeted organisms will include those implicated in the development of disease from the work in the above aims. Among the expected long-term benefits of this work will be the identification of organisms that can serve as predictors of intra-oral health and disease, and the development of broadly useful DNA microarray for microbial surveys and diagnostic studies.